362 MRS BULLETIN • VOLUME 30 • MAY 2005

IntroductionThe optical properties of metal nanopar-

ticles and their applications have been a topicof dramatically increasing interest overthe last several years. Much of this interestis generated by the growing expertise innanofabrication methods that enable moreand more possibilities of realizing metallicnanostructures of controlled size and shape.This has led to a proliferation of nanopar-ticle shapes such as rods,1 disks,2 rings,3cups,4 and cubes5 (see the introductory article

in this issue for illustrations of variousshapes). Advances in chemical synthesis arecomplemented by developments in planarnanostructure fabrication based on clean-room and hybrid techniques. These devel-opments, along with the addition of fast,accurate numerical methods for calculatingthe electromagnetic properties of nanoscalestructures,6–9 are providing us with usefulbuilding blocks for guiding, controlling,and manipulating light at the nanometer

scale, with metallic nanostructures asnanophotonic components.

In the past several years, it has becomeincreasingly apparent that by precisely con-trolling the dimensions of metallic nano-structures of certain specific shapes, one cancontrol the wavelengths at which they ab-sorb or scatter light. In all metallic nanopar-ticles, optical resonant behavior is due to thecollective electronic, or plasmon, resonanceof the metal. The plasmon resonance fre-quency in metals is a function not only of thetype of metal, but also, especially at thenanoscale, the shape of the metal. For solidmetallic nanospheres, the optical resonanceis essentially a fixed frequency resonance.Solid Au nanoparticles are well known toabsorb green light,10 and when embeddedin a glass matrix, they give rise to the beauti-ful deep red color known for centuries asruby glass.

Actually, the plasmon resonance of solidmetallic nanoparticles varies only weaklywith particle size, shifting to longer wave-lengths as the particle size is increased, and isalso sensitive to the dielectric environment ofthe nanoparticle. One nanoparticle geometrythat gives rise to some degree of shape tun-ability is that of a metallic nanorod, wherethe aspect ratio defines two distinct plasmonresonance frequencies associated with thelongitudinal and transverse dimensions ofthe nanostructure.11

Tunable Plasmons with NanoshellGeometry

Over the past few years, our research efforts have focused on metallic nano-structures of a spherical topology, but with asymmetric, dielectric core. Since the opticalproperties of this type of nanostructure aredependent upon the size and thickness ofthe metallic shell layer, we call this struc-ture a nanoshell.12 In this geometry, the plas-mon resonance frequency is determinedby the relative sizes of the inner and outerradii of the shell.13,14 By adjusting the relativecore and shell dimensions, gold or silvernanoshells can be fabricated that will absorbor scatter light at any wavelength acrossthe entire visible and infrared regions ofthe electromagnetic spectrum.15–18

In Figure 1a, the basic nanoshell geom-etry is illustrated; Figure 1b shows a con-centric nanoshell, or “nano-matryoshka,”so-named for its resemblance to Russiannesting dolls. Figure 1c shows a metallicnanorod. In Figure 1d, the dotted curve in-dicates the theoretical plasmon resonancewavelength of a nanoshell as a function ofthe nanoparticle’s core–shell ratio (r1/r2)for a nanoshell in the small size (dipole, orelectrostatic) limit. Also plotted here are arange of wavelengths that have been re-ported for nanorod resonances, where the

Playing withPlasmons: Tuning theOptical ResonantProperties ofMetallic Nanoshells

Naomi Halas

AbstractNanoshells, concentric nanoparticles consisting of a dielectric core and a metallic

shell, are simple spherical nanostructures with unique, geometrically tunable opticalresonances. As with all metallic nanostructures, their optical properties are controlled bythe collective electronic resonance, or plasmon resonance, of the constituent metal,typically silver or gold. In striking contrast to the resonant properties of solid metallicnanostructures, which exhibit only a weak tunability with size or aspect ratio, the opticalresonance of a nanoshell is extraordinarily sensitive to the inner and outer dimensions of the metallic shell layer.The underlying reason for this lies beyond classicalelectromagnetic theory, where plasmon-resonant nanoparticles follow a mesoscaleanalogue of molecular orbital theory, hybridizing in precisely the same manner as theindividual atomic wave functions in simple molecules.This plasmon hybridization pictureprovides an essential “design rule” for metallic nanostructures that can allow us toeffectively predict their optical resonant properties. Such a systematic control of the far-field optical resonances of metallic nanostructures is accomplished simultaneouslywith control of the field at the surface of the nanostructure.The nanoshell geometry is ideal for tuning and optimizing the near-field response as a stand-alone surface-enhanced Raman spectroscopy (SERS) nanosensor substrate and as a surface-plasmon-resonant nanosensor.Tuning the plasmon resonance of nanoshells into the near-infrared region of the spectrum has enabled a variety of biomedical applications that exploit the strong optical contrast available with nanoshells in a spectral region where blood and tissue are optimally transparent.

Keywords: bionanotechnology, nanoshells, nanophotonics, plasmonics, plasmons.

www.mrs.org/publications/bulletin

Playing with Plasmons:Tuning the Optical Resonant Properties of Metallic Nanoshells

MRS BULLETIN • VOLUME 30 • MAY 2005 363

longitudinal plasmon is shifted to longerwavelengths as its length is increased. Theexperimentally reported tunability rangeof nanoshells is plotted in the same figure.In this range, we have also included theexperimentally obtained resonances of con-centric nanoshells. The spectral range ac-cessible by the tunable plasmon resonanceof core–shell nanoparticles spans virtuallythe entire spectrum from visible light to thefar-infrared, and it is theoretically possiblethat an even broader range of tunabilitymay be achievable.

Our current method for fabricating nano-shells relies on a seeded metallization of afunctionalized silica nanoparticle core.12

The relatively straightforward synthesis ofhighly spherical and monodisperse silicananoparticles has been known for decades.19

The silica-core nanoparticles are first func-tionalized with aminopropyltriethoxysilane(APTES). This APTES functionalization per-mits the attachment of very small colloidalAu islands to the nanoparticle surface.Since the colloidal gold is highly charged,it covers the functionalized silica nano-particle surface until electrostatic repulsionlimits further deposition. This coverage isapproximately 25% of the nanoparticlesurface. Once the small Au islands havebeen attached to the nanoparticle’s surface,more gold is deposited onto the nanoparticle

surface using an electroless plating proce-dure. By careful control of the number ofislands and the amount of reductant used,one can control the thickness of the metalliclayer of the resulting nanoshells.

The tunability of the optical resonance ofnanoshells is quite remarkable, considering,for example, that if the core and shell ma-terials were inverted, this tunability wouldessentially disappear, and any wavelengthshift would arise purely from electromag-netic (phase retardation) effects. So what isthe essential characteristic of the metallicshell geometry that gives rise to this uniqueproperty?

Nanoshells are a specific example of ageneral principle for the design of plasmon-resonant nanostructures we refer to asplasmon hybridization (Figure 2).17 Essentially,the plasmon response of metal-basednanostructures can be understood as theinteraction or “hybridization” of plasmonssupported by metallic nanostructures ofmore elementary shapes. As an example,the plasmon hybridization picture can beused to describe the structural tunabilityof nanoshells as the interaction betweentwo fixed-frequency plasmons supportedby a nanoscale sphere and nanoscale cavity.Nanoshell plasmon tunability can be seenin light of this model, where the nanoshellplasmons correspond to the ��, or “bond-

ing,” plasmon and the higher-energy ��,or “anti-bonding,” plasmon. Only the lower-energy �� plasmon interacts strongly withan incident optical field. This simple pic-ture agrees quantitatively with classicalelectromagnetic (Mie scattering) theory, alsoexplaining why the nanoshell plasmonshifts to lower energies as the shell thick-ness is decreased. This trend is due to anincreased interaction between the sphereand cavity plasmons, resulting in increasedsplitting between the two hybrid plasmonsof the nanoshell. Plasmon hybridization isimportant because it provides us with asimple but powerful and general principlethat can be used to guide the design ofmetallic nanostructures and predict theirplasmon response qualitatively and quan-titatively. This can be seen in the case of the concentric nanoshell, whose complexplasmon response is due to the hybridiza-tion interaction between the inner and outernanoshell of this four-layer nanostructure.17

The optical properties of nanoshells alsovary with absolute nanoparticle size. Bykeeping the core–shell ratio constant butincreasing the total nanoparticle size, ad-ditional spectrally distinct multiple reso-nances appear in the nanoshell spectrum.20

Each of these resonances has a unique angular light-scattering signature that can easily be measured. Additionally, the

Figure 1. (a) Schematic illustration of asilica-core, gold-shell nanoshell,indicating inner (r1) and outer (r2) radiiof the shell layers. (b) Depiction of afour-layer, concentric nanoshell.(c) Schematic illustration of a metallicnanorod. (d) Plot of nanoshellresonance as a function of core andshell dimensions, overlaid with reportedspectral ranges of nanorod resonances(red, transverse plasmon; purple,longitudinal plasmon), and reportednanoshell and concentric nanoshellcombined spectral range of plasmonresponse.

Figure 2. Plasmon hybridization and the sphere–cavity model for nanoshells: the interactionbetween a sphere (resonance frequency, �sp) and a cavity plasmon (resonance frequency,�c) is tuned by varying the thickness of the shell layer of the nanoparticle.Two hybridplasmon resonances, the �� “bright,” or “bonding,” plasmon and the �� “dark,” or“anti-bonding,” plasmon resonances are formed.The lower-energy plasmon couples moststrongly to the optical field.

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Playing with Plasmons:Tuning the Optical Resonant Properties of Metallic Nanoshells

particle becomes a better scatterer than ab-sorber of light with increasing particle size,with the lowest-order plasmon modes be-coming the most strongly scattering rela-tive to the higher-order modes. Also, withincreasing nanoparticle size, an overallredshift in the hybridized plasmon modescan be seen, where the �– plasmon is morestrongly downshifted in energy than the�� plasmon is upshifted. This purely elec-tromagnetic effect is most easily observ-able in the multilayer nano-matryoshkaplasmon energies, where a redshift of allhybridized plasmon energies occurs.18

Therefore, in our current nanophotonics“toolbox,” there are two distinct physicalmechanisms that give rise to structuraltunability of the optical properties of indi-vidual nanoparticles. These are illustratedin Figure 3. As we have just seen, plasmonhybridization gives rise to tunable plas-monic nanoparticles. In contrast, semicon-ductor quantum dots are tunable excitonicnanoparticles, whose emission wavelengthis controlled by quantum confinement ofthe excitonic wave function within the nano-structure, which can be conceptually under-stood in a simple particle-in-a-box picture.21

It is quite useful to compare the propertiesof these two types of nanostructures.Nanoshells and quantum dots have manycomplementary optical properties: whilequantum dots are highly emissive fluoro-phores with high quantum efficiency,nanoshells, being metals, are essentiallynon-emissive. For metals, all the conductionelectrons participate in the plasmon exci-tation collectively, which leads to extremely

large optical absorption cross sections rel-ative to excitonic or molecular systems,where each photon interacts with a singleelectron–hole pair. Comparing single nano-shells to single quantum dots, nanoshellstypically have a 106 larger absorption crosssection, nominally five times the physicalcross section of the nanoparticle.

Surface-Enhanced RamanScattering Optimized onNanoshell Substrates

Since the internal geometry of a dielectriccore–metal shell nanoparticle controls thefar-field electromagnetic response, it fol-lows directly that the local electromag-netic field at the nanoshell surface is alsocontrolled by its geometry. The strong localfields at a metallic surface associated withits plasmon resonance are responsible forthe dramatic enhancements observed insurface-enhanced spectroscopies such asSERS,22–25 where molecules are bound toor in local contact with the metal surface. Ingeneral, the molecular resonance energyof the molecule and substrate–adsorbateinteractions known as “chemical effects”can also contribute to the overall enhance-ment in SERS. However, by judicious selection of the nonresonant adsorbatemolecule and the Raman pump laser wave-length, one can design a SERS responsethat is predominantly electromagnetic innature. Historically, the lack of reliable tech-niques for controlling the local nanoscaleelectromagnetic environment at the surfaceof macroscopic or mesoscopic metal struc-tures has been the fundamental experi-

mental limitation to the quantification andcontrol of these effects.

A striking example of this has been the numerous experiments reporting SERSenhancement factors of 1012–1015 obtainedfrom molecules adsorbed on surfaces ofaggregated gold and silver colloid films.24,26,27

In these investigations, the enormous en-hancements reported were attributed tolocalized plasmons, or “hot spots,” of ini-tially unknown local geometry that providethe appropriate electromagnetic nano-environment to produce the large enhance-ments observed.28 Subsequent investigationshave shown that the high-field intensitiesare most likely associated with junctions,or “dimer plasmons,” between two adja-cent nanoparticles.29–32 These types of ob-servations have spurred much interest anddevelopment of a variety of metallic nano-scale geometries for enhancing SERS, estab-lishing this as one of the primary researchareas within plasmonics.

We have recently investigated the core–shell geometry of a nanoshell for its poten-tial as a SERS substrate (Figure 4).33 Ourfocus has been on optimizing SERS in thenear-infrared region of the spectrum. Inprinciple, Raman spectroscopy at near-infrared wavelengths is highly desirable forprobing chemically complex environmentsbecause unwanted background fluorescencefrom molecules is drastically reduced. Also,Raman scattering is a much weaker effectat infrared wavelengths than when pumpedwith visible light, making a SERS substrateparticularly desirable for this wavelengthrange.

Figure 3. (a) Nanoshells are tunable plasmonic nanoparticles. Micrographs show a field of many nanoshells (large micrograph) and onenanoshell (small micrograph).Vials show nanoshells in solution. (b) Semiconductor quantum dots are tunable excitonic nanoparticles (courtesyof the Bawendi group). A field of quantum dots is displayed in the bottom image; an individual quantum dot is shown in the upper-left micrograph.Vials of quantum dots are also shown. Comparing single nanoshells to single quantum dots, nanoshells typically have a 106 larger absorptioncross section, nominally five times the physical cross section of the nanoparticle.

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MRS BULLETIN • VOLUME 30 • MAY 2005 365

To optimize the nanoshell geometry formaximum SERS enhancement, the plasmonresonance is tuned near the pump laserwavelength. In optimizing the near-fieldresponse at a selected wavelength, nano-shell size must also be considered. Since thesize of the core and the shell of a nanoshellcan be varied independently, we plot thenanoshell Raman response in “core–shellspace” to determine the optimum dimen-sions for a nanoshell with a maximum SERSenhancement at the pump laser wavelengthof choice. We have shown experimentallythat variation of the core diameter andshell layer thicknesses of a nanoshell can beused to “tune” the local electromagneticfield at the nanoparticle surface in a mannerthat directly controls the SERS response ofmolecules adsorbed on its surface.

The data obtained reveal excellent agree-ment between the electromagnetic field atthe nanoshell surface and Raman enhance-ments for the specific case of the nonresonantadsorbate molecule p-mercaptoaniline, withall apparent contributions to the SERS en-hancement due to the plasmon resonance ofthe individual nanoparticles. Figure 4 showsa SERS spectrum for p-mercaptoaniline onAg nanoshells in solution, where the SERSresponse was obtained using a 1.06 �m

Nd:YAG pump laser. The three Stokesmodes are shown both in the experimentalspectrum and in core–shell space. The ex-perimentally obtained enhancement wasdetermined in this case to be nominally106, which is limited in solution because the broad plasmon resonances of the nano-shells absorb the Stokes and anti-Stokeslight. More recent results in a film geometryhave shown that when absorption of the Stokes emission is minimized, sig-nificantly larger enhancements can be observed.34

Nanoshell Surface PlasmonResonance (SPR) Sensors

Nanoshells also provide a useful geo-metry for chemical sensing due to the sen-sitivity of the nanoshell plasmon resonanceto its local dielectric environment. It hasbeen observed that the nanoshell topologyhas enhanced sensitivity to changes in itsdielectric environment relative to a solidmetallic nanoparticle.35

The sensitivity of the nanoshell plasmonresonance to its dielectric environmentcan be understood in the context of thesphere–cavity model description of hy-bridized nanoshell plasmons (Figure 5).36

Of the two hybridized nanoshell plasmons,

the low-energy plasmon is more sphere-like, and the high-energy hybrid plasmonis more cavity-like. A change in the dielec-tric environment will primarily affect the more sphere-like resonance, ��, withonly a weak effect on the higher-energy res-onance, �� (Figure 5a). One can also inferfrom this picture that changes in the dielec-tric constant of the core will not affect ��

significantly.We have recently performed a theoretical

and experimental study of the geometricalfactors that optimize the nanoshell geometryfor greatest sensitivity to changes in its di-electric environment, essentially designingthe optimal nanoshell surface plasmonresonance (SPR) nanosensor.37 To investigatethe geometric factors affecting the sensi-tivity of a nanoshell SPR sensor, Mie scat-tering theory was used to calculate the ex-tinction cross section of nanoshells withvarying dimensions. Both the overall particlesize and the relative dimensions of theinner and outer core radii were varied in-dependently in this study. Since the ab-solute size of the nanoshell was includedin this study, multipolar plasmon effectswere also examined.

As the index of refraction of the sur-rounding medium is increased, two effects

Figure 4. (a) Surface-enhanced Raman scattering spectrum of p-mercaptoaniline on Ag nanoshells dispersed in solution and optimized for the1.06 �m pump laser wavelength. (b) Theoretical core–shell plots indicating maximum enhancement for each Stokes mode as a function of coreand shell dimensions for the stated pump laser wavelength.The lines at 65 nm and 79 nm denote selected core radii of nanoshells used in thisexperiment.

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Playing with Plasmons:Tuning the Optical Resonant Properties of Metallic Nanoshells

are observed: a shifting of the nanoshelldipolar plasmon to longer wavelengths(from �700 nm to 900 nm), and an in-crease in the quadrupole plasmon reso-nance relative to the dipole plasmonresonance in the nanoshell spectrum (ap-pearing as a shorter-wavelength shoulderon the dipole plasmon resonance). This isclearly observed experimentally (Fig-ure 5b). The strengthening of the quadru-pole plasmon resonance is due to phaseretardation effects: when the dielectric con-stant of the embedding medium is in-creased, the nanoparticle appears largerrelative to the reduced spatial wavelengthof the incident light. For convenience inthese measurements, nanoshells were dis-persed and bound to a glass substrate, fa-cilitating exposure to multiple solventsand rinsing procedures. This nanoshell filmpreparation produced films with plasmon-resonant properties remarkably similar toindividual nano-shells dispersed in solu-tion, so changes in the SPR wavelengthcould be followed precisely. A systematicreduction in the SPR shifts due to the pres-ence of the dielectric substrate of �25%,relative to solution-phase measurements,was noted. For the nanoshell geometry, itwas found that the magnitude of the SPRshift upon increase in the refractive indexof the embedding medium increases withthe overall size of the nanoparticle. TheSPR shift is also dependent upon thecore–shell ratio, and is most sensitive inthe thin-shell limit of the nanostructure’sinternal geometry.

Biomedical Applications ofNanoshells

Tuning the nanoshell resonance to thenear-infrared region of the spectrum, when

combined with the high biocompatibilitycharacteristic of gold, results in a combina-tion of features that are ideal for biomedicalapplications. The near-infrared region ofthe spectrum is the region of highest physio-logical transmissivity, where blood andtissue are most transparent and light canpenetrate tissue at distances of 10 cm ormore. This unique confluence of chemicaland optical properties has been exploitedin the development of several applicationsof nanoshells to problems in drug delivery,rapid whole-blood immunoassay, andminimally invasive cancer diagnostics andtherapeutics.

Temperature-sensitive polymers such ashydrogels, when raised above their lowestcritical solution temperature, can be made tocollapse to a small fraction of their initialvolume.38,39 Molecules that have been em-bedded in the voids of such a material can be released upon this thermal collapse.We recently constructed a composite material consisting of nanoshells embeddedin the temperature-sensitive material N-isopropylacrylamide-co-acrylamide(NIPAAm-co-AAm).40 In this type of com-posite material, optical illumination at theplasmon-resonant wavelength of the em-bedded nanoshells is sufficient to induce atemperature increase of several degrees inthe matrix surrounding the nanoshell. Inthis way, optical illumination can be usedto control the hydrogel’s photothermal col-lapse. This novel optomechanical materialcan be used for drug delivery, where re-lease of a drug embedded in the compos-ite can be induced by resonant laser illumination. Metallic nanoparticles at vari-ous optical resonances can be used to makevarious composites that are independ-ently optically addressable,41 for use in ap-

plications such as remote-access opticallyaddressable gates and valves.

Nanoshells have also been used in asimple aggregation immunoassay that canmeasure physiologically relevant concen-trations of analyte in whole blood with nosample preparation.42 Nanoshells with near-infrared plasmon resonances are conjugatedwith an antibody specific to the analyte ofinterest. When introduced into a wholeblood sample, aggregation of nanoshellswill begin to occur in the presence of theanalyte. The plasmon resonance of nano-shells is strongly modified by the aggrega-tion, shifting the plasmon resonance tolonger wavelengths. When the nanoshellresonances are tuned to near-infrared lightin a region of the spectrum where blood istransparent, the nanoshell aggregationthat signals the presence of the analyte canbe readily detected.

The photothermal response exploited inthe nanoshell–hydrogel composite drugdelivery material has also been exploredas a potential strategy for cancer therapy.43–45

By combining two benign moieties, near-infrared light and nanoshells, localized, irreversible photothermal ablation of tumortissue was successfully achieved both in vitro and in vivo.43

Cultured cells irradiated with very high dosages of near-infrared light main-tain viability without nanoshells present.Likewise, cells incubated with nanoshells inthe absence of laser irradiation maintainedtheir viability. However, combining nano-shells with infrared light exposure re-sulted in localized cell death in the regionof laser irradiation. Monitoring this experi-ment with an MRI-based temperature-mapping technique revealed that infraredlaser fluences that would normally induce

Figure 5. (a) Plasmon hybridization picture applied to surface plasmon resonance sensing with nanoshells: the low-energy “bonding” plasmon, �� , issensitized to changes in its dielectric environment.The blue background schematically denotes the embedding medium for the nanoparticle.(b) Experimental curves showing plasmon resonance shifts for nanoshell-coated films in various media: (i) carbon disulfide, (ii) toluene, (iii) hexane, (iv) ethanol, (v) H2O, and (vi) air. The index of refraction for each embedding medium is noted on the far right of the spectra. Spectraare offset for clarity. (c) Scanning electron micrograph of nanoshells deposited onto a poly(vinyl pyridine) functionalized glass surface, as used to acquire data in (b). Inset: individual nanoshell.

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MRS BULLETIN • VOLUME 30 • MAY 2005 367

temperature increases of less than 10�Cwithout nano-shells present produce tem-perature increases of more than 37�C forthe same exposure time. Nanoshells wereinitially injected into mouse tumors, where,following near-infrared laser irradiation,the tumor path-ology suggested that irre-versible tissue damage had coincidedwith the measured photothermal temper-ature increase in the region of the tumorwhere the illuminated nanoshells hadbeen embedded.

Following these initial studies, a study involving nanoshell-assisted photother-mal therapy in live mice with function-ing immune systems was also performed.45

In this work, tumors grown on the flanksof mice were treated by injecting nano-shells into the bloodstream of the mouse;over the following six hours, the nano-shells were passively taken into the tumorsite by means of the enhanced permeabil-ity and retention effect of the nanopar-ticles within the tumor. Tumors were thenilluminated through the animal’s skinwith a diode laser (808 nm, 4 W/cm2, 3min). All such treated tumors underwentcomplete remission, and the treated miceappeared healthy and tumor-free 90 dayslater. Control animals and additional ani-mals that had undergone laser treatmentwithout nano-shell injection had to be eu-thanized when their tumors increased to apredetermined size, which occurred 6–19days post-treatment. This simple, nonin-vasive treatment shows significant prom-ise as a technique for selective photothermaltumor ablation.

SummaryTunable plasmon-resonant nanoparticles

clearly have a broad range of applicationsboth as nanosensors, exploiting effectssuch as surface-enhanced Raman scatter-ing and surface plasmon resonance, andas nanoactuators, based on photothermaleffects. The ability to manipulate the opticalproperties within a single stand-alonenanoparticle geometry with high symmetrymakes analysis and optimization of many of these properties relatively straight-forward. We believe that nanoshells are aprime example of successfully designingand achieving function at the nanoscaleand clearly represent the extraordinary potential of plasmon-resonant nano-

photonic structures in nanoscience andnanotechnology.

AcknowledgmentsThe author gratefully wishes to acknowl-

edge the National Science Foundation, theArmy Research Office, the Air Force Officeof Scientific Research, the National Aero-nautics and Space Administration, theCongressionally Directed Medical ResearchProgram of the Department of Defense,the Texas Advanced Technology Program,and the Robert A. Welch Foundation fortheir generous support of these researchefforts. The author would especially liketo acknowledge the students, postdoctoralfellows, faculty colleagues, and collabora-tors and associates of the Laboratory forNanophotonics at Rice University for theirparticipation and collaboration in all theseresearch efforts.

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Three-Dimensional Multifunctional CeramicComposites Workshop October 3-5, 2005

Beckman InstituteUniversity of Illinois at Urbana-Champaign

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